Rotating machines, such as a centrifugal compressor, are used for turbo refrigerators or small-sized gas turbines. This rotating machine has the impeller in which a disc section fixed to the rotating shaft is provided with a plurality of blade sections. The rotating machine gives pressure energy and speed energy to gas by the impeller being rotated.
The impeller is attached to a rotor shaft by shrinkage fitting or the like. However, the unbalance of mass may occur in a circumferential direction due to the positional deviation of incorporation into the rotor shaft, a manufacturing error at the time of machining, or the like. For example, when the central axis of the mass of a rotary body is inclined with respect to the rotation center of the rotor shaft, a centrifugal force is generated by rotation whereby the unbalance of a moment or dynamic unbalance occurs. Therefore, since shaft vibration may increase, adjustment is performed in advance before an operation, such as at the time of manufacture, at the time of a test operation, or at the time of field installation.
Particularly, when the impeller is constituted of a single stage and has an overhang shaft structure, as in a speed increasing gear built-in type geared compressor, it is necessary to attach a weight for performing balance adjustment to an impeller.
Thus, in order to prevent vibration resulting from the unbalance of the rotary body, it is suggested that the blade sections of a fan or the impeller are supported and a plurality of balance holes with different depths are provided in an axial end surface of a tube portion of the disc section attached to the rotor shaft so as to perform balance adjustment. Moreover, it is suggested that balance adjustment is performed by appropriately mounting weights on the plurality of balance holes (for example, refer to Patent Documents 1 to 3).